The present invention relates to switching technology in a digital access network and more particularly to techniques for providing dynamic bandwidth switching functionality in an access network which supports only static or nailed up bandwidth switching.
The increasing demand for terminal user services has spurred rapid advances in the field of data communications. Initially, telecommunication services were provided to subscribers via individual copper wire lines connected between subscribers and the telephone exchanges. However, with the rapid increase in the number of subscribers, this approach soon became costly and unmanageable.
Driven by a desire to lower communication costs and to improve the quality of both transmission services and network management services, communication networks are increasingly using digital technology to transport voice, data, audio, video and other types of information to subscribers. Access networks and digital loop carrier (DLC) systems have been developed which further facilitate provision of services to subscribers. FIG. 1A depicts a conventional communication network 10 including an access network 14 coupled with a local digital switch (LDS) 12. LDS 12 may also be referred to as a central office (CO) switch and is usually a Class 4 or a Class 5 switch. LDS 12 typically performs bandwidth management and switching functions in order to provide services to subscribers 20. LDS 12 integrates access network 14 into a wider telecommunication network (not shown). Examples of LDS 12 include the 5ESS switch manufactured by Lucent, and the DMS 100 switch manufactured by Nortel.
Access network 14 is coupled with LDS 12 using communication links 16-1 and 16-2. In a specific embodiment, communication links 16-1 and 16-2 are T-1communication links which transport data using the DS-1 digital format. Several other types of communication links known in the art may also be used for communication links 16-1 and 16-2. The DS-1 format is the basic transmission format for digital communications. The DS-1 data format supports a bandwidth of 1.544 Mb/s and may be used to transport services of various types including voice, data, audio, video, and the other types of services known to those of ordinary skill in the art. Each DS-1 signal consists of 24 DS-0 channels each of which supports a bandwidth of 64 kb/s and represents a communication channel. Each DS-0 channel terminates in a network termination.
Access network 14 facilitates provision of services to subscribers 20. As shown, access network 14 comprises one or more remote terminals (RTs) 18-1, 18-2 coupled to LDS 12 via communication links 16-1 and 16-2, and coupled to subscribers 20 via subscriber links 28. The DS-0 channels of communication links 16-1 and 16-2 end at RTs 18-1 and 18-2 to form network terminations 22, while subscriber links 28 end in the RTs to form subscriber terminations 24. Each RT is responsible for establishing a communication path between LDS 12 and subscribers 20. Functions performed by each RT include demultiplexing the DS-0 channels received via the communication links, demodulating the digital signals received via communication links 16-1 and 16-2, providing connections between network terminations and subscriber terminations, and delivering services to and from subscribers 20. RTs may be placed at customer premises or in central offices.
In conventional systems like the one shown in FIG. 1A, the communication interface between LDS 12 and RTs 18-1 and 18-2 is generally based on a static bandwidth switching standard such as Bellcore""s well known TR-TSY-000008 (TR-8) standard. In order to support a static switching standard such as the TR-8 standard, LDS 12 must be TR-8 compliant and RTs 18-1 and 18-2 must be equipped with interface modules which support the TR-8 interface. According to the TR-8 standard each DS-0 channel within a DS-1 is dedicated to a particular subscriber. Accordingly, in order to provide a communication path between LDS 12 and a subscriber 20, according to the TR-8 standard a DS-0 network termination 22 of a DS-0 channel is xe2x80x9cnailed upxe2x80x9d or dedicated to a particular subscriber termination connected to the subscriber. In effect, a dedicated one-to-one relationship or a static relationship exists between a DS-0 channel from communication links 16-1 and 16-2 and a subscriber. TR-8 compliant RTs thus provide static bandwidth allocation.
As shown in FIG. 1A, nailed up connections 26 exist between network terminations 22 and subscriber termination 24 in the RTs. The provisioning of DS-0s for each of the subscribers and the nailing up of DS-0 network terminations with subscriber terminations is performed when access network 14 is configured, usually when the network is setup for providing services to subscribers 20. Typically, a network management station (not shown) is coupled to RTs 18-1 and 18-2 to facilitate provisioning of access network 14.
Due to the static nature of the connection between a DS-0 channel network termination and a subscriber termination, the number of subscribers which can be serviced by the RTs is dependent on the number of DS-0 channels between LDs 12 and the RTs. Thus, according to the TR-8 standard, a single DS-1 signal comprising 24 DS-0s can support a maximum of 24 subscribers. In order to support additional subscribers, additional DS-1 communication lines must be leased from the communications exchange provider managing LDS 12. Thus, as shown in FIG. 1A, each RT which is connected to a DS-1 channel supports up to 24 subscribers. In order to support additional subscribers, for example subscribers 25 through 48, a second DS-1 communication link 16-2 is required. Leasing additional communication links is usually expensive and thus presents a financial obstacle for increasing the number of subscribers serviced by access network 14.
The use of static switching standards, such as the TR-8 standard, also result in under-utilization of communication links"" bandwidth capacity. For example, a DS-0 which has been dedicated to a particular subscriber termination cannot be used to communicate data to another subscriber even when the subscriber to which the DS-0 channel is dedicated is not utilizing the DS-0 channel. This results in wastage of valuable bandwidth resources.
Due to the limitations inherent in static switching techniques, several new standards, for example Bellcore""s TR-TSY-000303 (TR-303) standard, are being developed which allow dynamic switching between communication channels and subscribers. Dynamic switching mechanisms such as the TR-303 standard eliminate the concept of xe2x80x9cnailed upxe2x80x9d or dedicated connections between network terminations and subscriber terminations. In order to support a dynamic switching standard such as the TR-303 standard, LDS 12 must be TR-303 compliant and all RTs connected to the LDS must be equipped with an interface module which supports the dynamic switching or TR-303 interface.
FIG. 1B depicts a communication network 30 comprising an access network 34 coupled with LDS 32 which supports a dynamic switching standard, such as the TR-303 standard. Access network 34 includes one or more RTs 36 (only one of which is shown) which support a TR-303 standard. RT 36 is connected to TR-303 compliant LDS 32 via communication link 16-1, and to subscribers 20 via subscriber links 28. RT 36 thus provides network terminations 22 for the DS-0 channels of communication link 16-1 and subscriber terminations 24 for subscriber links 28. As in FIG. 1A, communication link 16-1 is typically a T-1 link and supports the DS-1 digital format. However, unlike FIG. 1A, there are no nailed up connections between network terminations 22 and subscriber terminations 24. According to the TR-303 standard, a connection between a DS-0 network termination and a subscriber termination is made at run time when RT 36 receives a request to establish a communication path between a DS-0 channel coupled to the network termination and a subscriber connected to the subscriber termination. RT 36 may receive connection requests from a subscriber, for example when a subscriber telephone goes off-hook, or from LDS 32 requesting a connection to a particular subscriber.
In order to facilitate dynamic link switching under the TR-303 standard, each subscriber termination is assigned a unique Call Reference Value (CRV) which uniquely identifies the subscriber termination and the properties of the subscriber connected to the subscriber termination. These properties include attributes of subscriber link 28 connected to the subscriber termination, the signaling mechanism, or the loop-start or ground-start properties. CRVs are unique per TR-303 interface. CRVs are allocated for the subscriber terminations when access network 34 is provisioned, usually at network set-up time. As previously stated, a network management station (not shown) coupled with RT 36 facilitates the provisioning process. The CRV information is also forwarded to LDS 32. Thus, the CRV information is stored by RT 36 and by LDS 32 and is used to facilitate dynamic connections between LDS 32 and subscribers 20.
Upon receiving a request to connect to a particular subscriber serviced by RT 36, LDS 32 determines the CRV for the subscriber termination connected to the subscriber. LDS 32 then allocates one or more xe2x80x9cavailablexe2x80x9d DS-0 channels in the DS-1 communication link 16-1 for the connection. DS-0 channels are available if they are not currently being used for providing connections. A connection request including information regarding the allocated DS-0s and the CRV information is then forwarded to RT 36. RT 36 then provides connection between the network terminations corresponding to the DS-0s allocated by LDS 32 and the subscriber termination identified by the CRV information. In this manner, the connection between the network terminations and the subscriber termination is provided dynamically during run time. The DS-0 channels allocated by LDS 32 for the connection may be reused when the present connection has been terminated.
Connection requests may also be initiated by subscribers 20. When a particular subscriber requests a connection, RT 36 intercepts the connection request and determines the CRV information for the subscriber termination connected to the requesting subscriber. The CRV information is sent to LDS 32 which allocates one or more available DS-0s for the connection. RT 36 then dynamically provides a connection between the network terminations of the allocated DS-0 channels and the requesting subscriber termination.
Using dynamic switching standards such as the TR-303 standard, the number of subscribers 20 supported by a RT may exceed the number of DS-0 channels connected to the RT 36, since not all the subscribers are connected at the same time. This is a substantial improvement over the TR-8 wherein the number of subscribers supported by an RT is limited by the number of DS-0 channels connected to the RT. As shown in FIG. 1B, using a TR-303 compliant LDS and an RT 36 which supports the TR-303 standard, more than 24 subscribers may be supported using a single DS-1 communication link 16-1. This is an improvement over access network 14 shown in FIG. 1A wherein only a maximum of 24 subscribers could be supported using a single DS-1 channel. In general, by using a dynamic switching standard such as the TR-303 standard, xe2x80x9csubscriber concentrationxe2x80x9d may be provided wherein the number of subscribers supported by an RT is greater than the number of DS-0 channels connected to the RT. Dynamic switching also promotes efficient utilization of bandwidth resources since it allows for reuse of available DS-0 channels to connect to the subscriber terminations.
Although dynamic switching standards, such as the TR-303 standard, alleviate many of the limitations associated with static switching standards, they have not been readily adopted by the service providers. This is due to the fact that a majority of the RTs, such as D-4 channel banks, which are currently in use and which have been installed by the service providers at significant costs support only the older TR-8 static standard and not the new TR-303 dynamic standard. For most service providers it would be cost prohibitive and not feasible to replace existing TR-8 compliant infrastructure with a TR-303 compliant infrastructure. Consequently, a majority of the existing access networks cannot enjoy benefits offered by dynamic switching techniques.
Accordingly, there is a need for a system and method which allows communication networks supporting static switching techniques only to enjoy the advantages provided by dynamic switching techniques. It is desired that existing TR-8 compliant systems be able to take advantage of the dynamic switching techniques provided by the TR-303 standard in a cost effective manner. It is also desired that the dynamic switching capability be provided without replacing or substantially modifying the existing networks supporting static switching standards in order to minimize the costs associated with replacing network equipment.
According to the invention, a system and method provide dynamic switching functionality in an access network which supports only static switching. The present invention uses dynamic switching techniques to provide communication channels between a local digital switch and subscribers of the access network who are connected to remote terminals which support only static switching.
According to one aspect of the present invention, the dynamic switching functionality is provided by a dynamic switching subsystem which is coupled with the local digital switch via a first communication link and coupled with a remote terminal via a second communication link. The dynamic switching subsystem provides a first set of network terminations for communication channels within the first communication link and a second set of network terminations for communication channels within the second communication link. The remote terminal provides a third set of network terminations for communication channels received from the dynamic switching subsystem and subscriber terminations for subscribers connected to the remote terminal. Since the remote terminal supports only static switching, nailed up connections are provided between the third network terminations and the subscriber terminations. According to the present invention, dynamic switching functionality is provided by performing dynamic switching between the first set of network terminations and the second set of network terminations when connection requests are received by the dynamic switching subsystem.
According to another aspect of the present invention, to facilitate dynamic switching between the first set of network terminations and the second set of network terminations, network termination call reference values are assigned to each of the second set of network terminations. The network termination call reference values uniquely identify communication channels from the dynamic switching subsystem to the remote terminal and which are nailed up by the remote terminal to the subscriber terminations. The dynamic switching subsystem uses the network termination call reference values to provide dynamic connections between the first set of network terminations and the second set of network terminations.
According to still another aspect of the present invention, a network management station may be provided to facilitate provisioning of the access network, including assigning network termination call reference values to the second set of network terminations. The network management station may also be configured to provide nailed up connections between the third set of network terminations and the subscriber terminations in the remote terminals.
The dynamic switching techniques of the present invention enable access networks to enjoy benefits offered by dynamic switching techniques without replacing existing static switching components and without incurring substantial replacement costs. The present invention allows access networks to provide xe2x80x9csubscriber concentrationxe2x80x9d whereby the number of subscribers serviced by the access network may exceed the number of communication channels leased from the local digital switch to the access network.
The invention will be better understood by reference to the following detailed description and accompanying figures.